1. Field of the Invention
The present invention relates in general to a screening machine for screening objects of different sizes and more particularly to a screening machine for screening architectural wastes generated when buildings are pulled down, various mixed wastes including wastes from households and offices, and sticky wastes such as leftovers from restaurants, as well as compost, bark, wood chips from sawmills, soil, rubble, etc. depending on their sizes.
2. Prior Art
As a conventional waste screening machine of this kind, the applicant of the present invention has proposed a screening machine which feeds large objects over a plurality of rotary spiral members arranged parallel to one another in the rotation direction thereof, allows medium-sized and small objects to drop between the spiral members, then allows small objects to drop through a porous screen, and discharges medium-sized objects sideways by using the spiral members (Japanese Laid-open Patent Publication No. 4-176374). As shown in FIG. 18, this machine comprises a plurality of spiral members 013 arranged in a plane at a frame opening 012, the bottom of which is covered with a screen 011 for screening small waste objects W1. The spiral members rotate to convey large wastes W3 to the discharge side of the machine and allow small and medium-sized wastes W1 and W2 to drop through the gaps between the spiral members 013, 013, and also allow small wastes W1 through the screen 011, then discharge wastes W2 remaining on the screen 011 in the spiraling direction of the spiral member. This machine has been favorably accepted by architectural waste treatment contractors.
Various ropes, cords and tapes included in wastes to be screened may wind around the spiral members. To remove such ropes, etc. machine operation must be stopped occasionally. Furthermore, since damp or wet leftovers or compost included in wastes tends to clog the screen, it is apprehended that minute particles such as soil cannot be separated by screening.